Spectroscopic Characterization of Dissolved Organic Matter: Insights Into the Linkage Between Sources and Chemical Composition

This dissertation investigated the chemical structure of DOM by advanced solid-state nuclear magnetic resonance (NMR) spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) techniques, as well as isotopic measurements and UV-visible spectroscopy, to shed light on the linkages between DOM sources and DOM composition. Unique and extensive sets of DOM samples studied here were isolated from various aquatic systems, covering end-member environments in which DOM is considered either microbially derived or terrestrially derived, and areas in which DOM has characteristics intermediate between the two end members. Important insights into specific site-related questions were also gained such as the fate of terrestrial DOM in the marine system, the seasonal variability in chemical structure of DOM in the Yukon River, and the chemical structure of DOM in lakes driven by hydrology. First, the presence of CRAM as the major structural units in DOM samples from the Penobscot River to Gulf of Maine transect and the Pacific Ocean implied that CRAM may cycle on time scales long enough to be transported into the ocean. Second, whereas spring DOM from the Yukon River was more enriched in lignin residues and carbohydrates than summer-fall and winter DOM, DOM samples across seasons shared relatively more refractory components such as CRAM, and nonprotonated OC and OCO pool. Third, CRAM occurred as the major component in three different lakes, though there was a selective loss of terrestrially derived DOM such as aromatics with increasing lake water residence time. Lastly, the ubiquity of CRAM in DOM from microbially and terrestrially derived end members and understudied environments like groundwaters was further confirmed by NMR spectroscopy coupled with FT-ICR mass spectrometry. The research in my dissertation clearly revealed the ubiquity of CRAM in DOM from vastly different environments with different source strengths. This implicates the chemical homogenization of DOM relative to source material in aquatic environments under the influence of diagenetical degradation processes